Field of the Invention
The present invention relates to an imaging device and a method of driving an imaging device.
Description of the Related Art
If a moving image and a still image can be shot at the same time with one camera, not only can a shooting scene be viewed as a moving image, but also a decisive scene in the moving image can be seen as a still image for fun. This can significantly enhance the values of shot images. Further, if a moving image at a normal frame rate and a moving image at a high frame rate can be shot at the same time with one camera, a specific scene can be switched to a slow-motion moving image to enjoy the image as a high-definition moving image. This can give a viewer an uplifting feeling.
Further, as a technique for making a movie or a TV image more realistic, there is an HDR (High Dynamic Range) technique for the moving image. This is to synthesize outputs from two pixel groups different in sensitivity to expand the reproduction range of luminance on a display screen in order to make the movie or the TV image realistic more than that in the conventional mainly by increasing instantaneous or partial luminance.
As an imaging device used to shoot such an image, there is proposed an imaging device using an imaging element having pixels including a plurality of photoelectric conversion units different in light-receiving efficiency. Japanese Patent Application Laid-Open No. 2014-048459 discloses an imaging device with a pair of photodiodes having asymmetric pupil shapes provided in each pixel. In the imaging device described in Japanese Patent Application Laid-Open No. 2014-048459, one of the pair of photodiodes is high in light-receiving efficiency and the other photodiode is low in light-receiving efficiency. Two signals from the pair of photodiodes are used as different image data to enable simultaneous shooting of two images.
However, in the imaging device that performs simultaneous shooting of two images, it is necessary to read out a plurality of images based on signals different in accumulation time within one frame period. If it takes time to read out these signals, the time required for one frame period will be long, resulting in a decrease in frame rate.